Ukraine's justice minister has threatened to declare a state of emergency if anti-government protesters in Kiev do not leave the ministry's headquarters.

The activists seized the ministry of justice building in the capital late on Sunday without resistance before setting up barricades outside with bags of snow.

Justice minister Olena Lukash, who is a participant in negotiations between the opposition and president Viktor Yanukovych aimed at ending months of violent protests against his rule, told local television she would ask for the talks to be broken off if the building was not cleared.

"I will be forced to ask the president of Ukraine to stop the talks if the building is not freed immediately and negotiators are not given a chance to find a peaceful solution to the conflict," Ms Lukash told the Inter channel.

She also warned that if the protesters did not leave the building she would also approach Ukraine's national security council with "a demand to discuss imposing a state of emergency in this country".

The radical activists, from a group named Spilna Sprava (The Right Deed), broke windows on the building and destroyed its official sign.

Ms Lukash said they had sprayed water inside in freezing temperatures, "turning it into a veritable ice rink".

The Interfax-Ukraine news agency said opposition leader and former boxing champion Vitali Klitschko, who is involved in the negotiations with the president, had visited the scene overnight and asked the protesters to leave, but to no avail.

Police have opened a criminal investigation into the seizure of a state building.

The presidency has offered the opposition a range of concessions, including a change in the constitution and the post of prime minister, to end the crisis.

According to officials, three people have already been shot dead in clashes with police forces in the last week although activists say the toll is six.

'Tough and cruel' police disperse protesters outside Kiev

While thousands of people continue protests in Kiev, Ukrainian police have arrested dozens of protesters who were trying to seize regional government headquarters in Mr Yanukovych's eastern heartland.

Local media reports said 37 protesters were arrested in Dnipropetrovsk, 30 in Zaporizhya, 12 in Cherkasy and 11 in Sumy following clashes with security forces that mirrored developments in the protest epicentre in Kiev.

In Sumy, eyewitnesses said police used heavy-handed tactics, beating activists who had occupied the regional administration building.

They said police had initially asked the protesters to leave the offices peacefully and most had done so before a sudden raid.

Several injuries have also been reported in different regions - among both protesters and the police - particularly in Dnipropetrovsk and Zaporizhya.

All the local government offices in largely pro-opposition western Ukraine - except for the Transcarpathia region - have already been occupied over the past few days.

Ukrainian police on Sunday dispersed thousands of protesters who had rallied in the south-eastern region of Zaporozhiya in a bid to capture to a regional administration building.

The Berkut (anti-riot police) cleared the square. Everything was very tough and cruel

Journalist Maxim Shcherbin

"Thanks to the measures taken, the attempt was thwarted," a statement by regional police said, adding that 3,000 protesters were involved in the action.

Local journalists wrote on Facebook that police used stun grenades and batons to disperse the protest, leaving many injured.

"The Berkut (anti-riot police) cleared the square. Everything was very tough and cruel," wrote journalist Maxim Shcherbin on his Facebook page.

Activists have stormed and held regional administration buildings in western Ukraine over the past days as part of the nationwide protests against Mr Yanukovych's rule.

The protests have now spread further east into areas where the president was once seen as having strong support in a major new headache for the embattled government.

"The police used their batons to drive people out of the shopping centre where the protesters were warming themselves and then launched a total clean up operation," local protest leader Igor Andrushchenko told pro-protest web channel Espreso TV.

Last week anti-government activists occupied the ministry of agriculture and, for a short while, the energy ministry.